Defeating Radiation Damping and Magnetic Field Inhomogeneity with Spatially Encoded Noise

Abstract

A simple NMR experiment capable of providing well resolved spectra under conditions where either radiation damping or static magnetic field inhomogeneity would broaden otherwise high-resolution NMR spectra is introduced. The approach involves using a strong pulsed magnetic field gradient and a selective radio-frequency pulse to encode a predetermined noise pattern into the spatial distribution of magnetization. Following readout in a much smaller field gradient, the noise sequence may be deconvolved from the acquired data and a high-resolution spectrum is obtained, eliminating the effects of either radiation damping or the static field inhomogeneity. In the presence of field inhomogeneity a field map is also obtained from the same single transient. A quasi-two-dimensional version of the experiment eliminates the need for deconvolution and produces improved results with simplified processing, but without requiring a full two-dimensional experiment. Example spectra are shown for both radiation damping and one-dimensional field inhomogeneity with improvement in linewidths of more than a factor of 40.

Characterization and Suppression Techniques for Degree of Radiation Damping in Inversion Recovery Measurements

“…We will utilize gradient inversion recovery (GIR), which uses a magnetic field gradient to continuously suppress any transverse magnetization during the evolution time (Sklenar 1995). There is a third class of suppression techniques, but these techniques are used to suppress RD during spectroscopy by greatly attenuating the transverse magnetization during acquisition (Michal 2010;Khitrin & Jerschow 2012) and are not useful for relaxometry experiments. Hardware solutions may be practical for some facilities, but many locations such as primarily undergraduate institutions lack the technical resources to modify the NMR spectrometer in the ways necessary to enact such suppression techniques.…”

Radiation damping in modern NMR experiments: Progress and challenges

“…Both these hardware based approaches are successful in eliminating RD to a large extent. Pulse sequence based eliminations include use of selective pulses to compensate for noise modulations [72,127,128]. In general all these approaches are fairly successful in their respective applications, yet none of them seems to have been adopted for use on a routine basis.…”

“…Recently Michal [128] developed a method to control radiation damping with spatially-encoded noise. The method is based upon the encoding of a structured pattern of noise into the spatial distribution of magnetization and was inspired by an optical spectroscopy technique known as noise autocorrelation spectroscopy with coherent Raman scattering (NASCARS) [136].…”

Effects of radiation damping for biomolecular NMR experiments in solution: A hemisphere concept for water suppression

“…Even residual, but sufficiently abundant, water protons induce a voltage in the coil and cause an electromagnetic field that nutates the magnetization back toward the 1Z axis (16)(17)(18)(19)(20)(21)(22)(23). Instrumental techniques to reduce apparent radiation damping and the NMR processing schemes to read out the effect have been developed (24)(25)(26)(27)(28)(29). However, it is known that even a pure 2Z magnetization can cause radiation damping by leakage of applied radio-frequency field or thermal noise fluctuation of the coil (18,(30)(31)(32).…”